RFID integrated circuit identifier self-check

ABSTRACT

A Radio Frequency Identification (RFID) tag IC stores an identifier and a check code. The IC determines whether the stored identifier is corrupted by comparing it to the check code. If the stored identifier does not correspond to the check code then the IC may terminate operation or indicate an error. The IC may also reconstruct the correct identifier from the check code.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/959,153 filed on Dec. 4, 2015, now U.S. Pat. No. 9,454,680, which isa continuation of U.S. application Ser. No. 13/865,993 filed on Apr. 18,2013, now U.S. Pat. No. 9,239,941, which claims the benefit of U.S.Provisional Patent Application Ser. No. 61/723,944 filed on Nov. 8,2012. The disclosures of the applications are hereby incorporated byreference for all purposes.

BACKGROUND

Radio-Frequency Identification (RFID) systems typically include RFIDreaders, also known as RFID reader/writers or RFID interrogators, andRFID tags. RFID systems can be used in many ways for locating andidentifying objects to which the tags are attached. RFID systems areuseful in product-related and service-related industries for trackingobjects being processed, inventoried, or handled. In such cases, an RFIDtag is usually attached to an individual item, or to its package.

In principle, RFID techniques entail using an RFID reader to interrogateone or more RFID tags. The reader transmitting a Radio Frequency (RF)wave performs the interrogation. The RF wave is typicallyelectromagnetic, at least in the far field. The RF wave can also bepredominantly electric or magnetic in the near field. The RF wave mayencode one or more commands that instruct the tags to perform one ormore actions.

A tag that senses the interrogating RF wave may respond by transmittingback another RF wave. The tag either generates the transmitted back RFwave originally, or by reflecting back a portion of the interrogating RFwave in a process known as backscatter. Backscatter may take place in anumber of ways.

The reflected-back RF wave may encode data stored in the tag, such as anumber. The response is demodulated and decoded by the reader, whichthereby identities, counts, or otherwise interacts with the associateditem. The decoded data can denote a serial number, a price, a date, adestination, other attribute(s), any combination of attributes, and soon. Accordingly, when a reader receives tag data it can learn about theitem that hosts the tag and/or about the tag itself.

An RFID tag typically includes an antenna section, a radio section, apower-management section, and frequently a logical section, a memory, orboth. In some RFID tags the power-management section included an energystorage device such as a battery. RFID tags with an energy storagedevice are known as battery-assisted, semi-active, or active tags. OtherRFID tags can be powered solely by the RF signal they receive. Such RFIDtags do not include an energy storage device and are called passivetags. Of course, even passive tags typically include temporary energy-and data/flag-storage elements such as capacitors or inductors.

BRIEF SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended asan aid in determining the scope of the claimed subject matter.

Embodiments are directed to an RFID tag integrated circuit (IC) thatstores an identifier and a check code. The IC may determine whether thestored identifier is corrupted by comparing it to the check code. If thestored identifier does not correspond to the check code, the IC mayterminate operation and/or indicate an error. The IC may alsoreconstruct the correct identifier from the check code.

These and other features and advantages will be apparent from a readingof the following detailed description and a review of the associateddrawings. It is to be understood that both the foregoing generaldescription and the following detailed description are explanatory onlyand are not restrictive of aspects as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The following Detailed Description proceeds with reference to theaccompanying drawings, in which:

FIG. 1 is a block diagram of components of an RFID system.

FIG. 2 is a diagram showing components of a passive RFID tag, such as atag that can be used in the system of FIG. 1.

FIG. 3 is a conceptual diagram for explaining a half-duplex mode ofcommunication between the components of the RFID system of FIG. 1.

FIG. 4 is a block diagram showing a detail of an RFID tag, such as theone shown in FIG. 2.

FIGS. 5A and 5B illustrate signal paths during tag-to-reader andreader-to-tag communications in the block diagram of FIG. 4.

FIG. 6 illustrates an identifier and a check code stored in an RFID tagIC according to embodiments.

FIGS. 7A-B are flowcharts depicting processes for identifier self-checkaccording to embodiments.

FIG. 8 is a flowchart depicting a process for identifier self-check andcorrection according to embodiments.

DETAILED DESCRIPTION

In the following detailed description, references are made to theaccompanying drawings that form a part hereof, and in which are shown byway of illustration specific embodiments or examples. These embodimentsor examples may be combined, other aspects may be utilized, andstructural changes may be made without departing from the spirit orscope of the present disclosure. The following detailed description istherefore not to be taken in a limiting sense, and the scope of thepresent invention is defined by the appended claims and theirequivalents.

As used herein, “memory” is one of ROM, RAM, SRAM, DRAM, NVM, EEPROM,FLASH, Fuse, MRAM, FRAM, and other similar information-storagetechnologies as will be known to those skilled in the art. Some portionsof memory may be writeable and some not. “Command” refers to a readerrequest for one or more tags to perform one or more actions. “Protocol”refers to an industry standard for communications between a reader and atag (and vice versa), such as the Class-1 Generation-2 UHF RFID Protocolfor Communications at 860 MHz-960 MHz by EPCglobal, Inc. (“Gen2Specification”), version 1.2.0 of which is hereby incorporated byreference.

FIG. 1 is a diagram of the components of a typical RFID system 100,incorporating embodiments. An RFID reader 110 transmits an interrogatingRF signal 112. RFID tag 120 in the vicinity of RFID reader 110 sensesinterrogating RF signal 112 and generate signal 126 in response. RFIDreader 110 senses and interprets signal 126. The signals 112 and 126 mayinclude RF waves and/or non-propagating RF signals (e.g., reactivenear-field signals)

Reader 110 and tag 120 communicate via signals 112 and 126. Whencommunicating, each encodes, modulates, and transmits data to the other,and each receives, demodulates, and decodes data from the other. Thedata can be modulated onto, and demodulated from, RF waveforms. The RFwaveforms are typically in a suitable range of frequencies, such asthose near 900 MHz, 13.56 MHz, and so on.

The communication between reader and tag uses symbols, also called RFIDsymbols. A symbol can be a delimiter, a calibration value, and so on.Symbols can be implemented for exchanging binary data, such as “0” and“1”, if that is desired. When symbols are processed by reader 110 andtag 120 they can be treated as values, numbers, and so on.

Tag 120 can be a passive tag, or an active or battery-assisted tag(i.e., a tag having its own power source). When tag 120 is a passivetag, it is powered from signal 112.

FIG. 2 is a diagram of an RFID tag 220, which may function as tag 120 ofFIG. 1. Tag 220 is drawn as a passive tag, meaning it does not have itsown power source. Much of what is described in this document, however,applies also to active and battery-assisted tags.

Tag 220 is typically (although not necessarily) formed on asubstantially planar inlay 222, which can be made in many ways known inthe art. Tag 220 includes a circuit which may be implemented as an IC224. In some embodiments IC 224 is implemented in complementarymetal-oxide semiconductor (CMOS) technology. In other embodiments IC 224may be implemented in other technologies such as bipolar junctiontransistor (BJT) technology, metal-semiconductor field-effect transistor(MESFET) technology, and others as will be well known to those skilledin the art. IC 224 is arranged on inlay 222.

Tag 220 also includes an antenna for exchanging wireless signals withits environment. The antenna is often flat and attached to inlay 222. IC224 is electrically coupled to the antenna via suitable antenna contacts(not shown in FIG. 2). The term “electrically coupled” as used hereinmay mean a direct electrical connection, or it may mean a connectionthat includes one or more intervening circuit blocks, elements, ordevices. The “electrical” part of the term “electrically coupled” asused in this document shall mean a coupling that is one or more ofohmic/galvanic, capacitive, and/or inductive.

IC 224 is shown with a single antenna port, comprising two antennacontacts electrically coupled to two antenna segments 227 which areshown here forming a dipole. Many other embodiments are possible usingany number of ports, contacts, antennas, and/or antenna segments.

In operation, the antenna receives a signal and communicates it to IC224, which both harvests power and responds if appropriate, based on theincoming signal and the IC's internal state. If IC 224 uses backscattermodulation then it responds by modulating the antenna's reflectance,which generates response signal 126 from signal 112 transmitted by thereader. Electrically coupling and uncoupling the antenna contacts of IC224 can modulate the antenna's reflectance, as can varying theadmittance of a shunt-connected circuit element which is coupled to theantenna contacts. Varying the impedance of a series-connected circuitelement is another means of modulating the antenna's reflectance.

In the embodiment of FIG. 2, antenna segments 227 are separate from IC224. In other embodiments the antenna segments may alternatively beformed on IC 224. Tag antennas according to embodiments may be designedin any form and are not limited to dipoles. For example, the tag antennamay be a patch, a slot, a loop, a coil, a horn, a spiral, or any othersuitable antenna.

The components of the RFID system of FIG. 1 may communicate with eachother in any number of modes. One such mode is called full duplex.Another such mode is called half-duplex, and is described below.

FIG. 3 is a conceptual diagram 300 for explaining half-duplexcommunications between the components of the RFID system of FIG. 1, inthis case with tag 120 implemented as passive tag 220 of FIG. 2. Theexplanation is made with reference to a TIME axis, and also to a humanmetaphor of“talking” and “listening”. The actual technicalimplementations for “talking” and “listening” are now described.

RFID reader 110 and RFID tag 120 talk and listen to each other by takingturns. As seen on axis TIME, when reader 110 talks to tag 120 thecommunication session is designated as “R→T”, and when tag 120 talks toreader 110 the communication session is designated as “T→R”. Along theTIME axis, a sample R→T communication session occurs during a timeinterval 312, and a following sample T→R communication session occursduring a time interval 326. Of course interval 312 is typically of adifferent duration than interval 326—here the durations are shownapproximately equal only for purposes of illustration.

According to blocks 332 and 336, RFID reader 110 talks during interval312, and listens during interval 326. According to blocks 342 and 346,RFID tag 120 listens while reader 110 talks (during interval 312), andtalks while reader 110 listens (during interval 326).

In terms of actual behavior, during interval 312 reader 110 talks to tag120 as follows. According to block 352, reader 110 transmits signal 112,which was first described in FIG. 1. At the same time, according toblock 362, tag 120 receives signal 112 and processes it to extract dataand so on. Meanwhile, according to block 372, tag 120 does notbackscatter with its antenna, and according to block 382, reader 110 hasno signal to receive from tag 120.

During interval 326, tag 120 talks to reader 110 as follows. Accordingto block 356, reader 110 transmits a Continuous Wave (CW) signal, whichcan be thought of as a carrier that typically encodes no information.This CW signal serves both to transfer energy to tag 120 for its owninternal power needs, and also as a carrier that tag 120 can modulatewith its backscatter. Indeed, during interval 326, according to block366, tag 120 does not receive a signal for processing. Instead,according to block 376, tag 120 modulates the CW emitted according toblock 356 so as to generate backscatter signal 126. Concurrently,according to block 386, reader 110 receives backscatter signal 126 andprocesses it.

FIG. 4 is a block diagram showing a detail of an RFID IC, such as IC 224in FIG. 2. Electrical circuit 424 in FIG. 4 may be formed in an IC of anRFID tag, such as tag 220 of FIG. 2. Circuit 424 has a number of maincomponents that are described in this document. Circuit 424 may have anumber of additional components from what is shown and described, ordifferent components, depending on the exact implementation.

Circuit 424 shows two antenna contacts 432, 433, suitable for couplingto antenna segments such as segments 227 of RFID tag 220 of FIG. 2. Whentwo antenna contacts form the signal input from and signal return to anantenna they are often referred-to as an antenna port. Antenna contacts432, 433 may be made in any suitable way, such as from metallic pads andso on. In some embodiments circuit 424 uses more than two antennacontacts, especially when tag 220 has more than one antenna port and/ormore than one antenna.

Circuit 424 also includes signal-routing section 435 which may includesignal wiring, a receive/transmit switch that can selectively route asignal, and so on.

Circuit 424 also includes a rectifier and PMU (Power Management Unit)441 that harvests energy from the RF signal received by antenna 227 topower the circuits of IC 424 during either or both reader-to-tag (R→T)and tag-to-reader (T→R) sessions. Rectifier and PMU 441 may beimplemented in any way known in the art.

Circuit 424 additionally includes a demodulator 442 that demodulates theRF signal received via antenna contacts 432, 433. Demodulator 442 may beimplemented in any way known in the art, for example including a slicer,an amplifier, and so on.

Circuit 424 further includes a processing block 444 that receives theoutput from demodulator 442 and performs operations such as commanddecoding, memory interfacing, and so on. In addition, processing block444 may generate an output signal for transmission. Processing block 444may be implemented in any way known in the art, for example bycombinations of one or more of a processor, memory, decoder, encoder,and so on.

Circuit 424 additionally includes a modulator 446 that modulates anoutput signal generated by processing block 444. The modulated signal istransmitted by driving antenna contacts 432, 433, and therefore drivingthe load presented by the coupled antenna segment or segments. Modulator446 may be implemented in any way known in the art, for exampleincluding a switch, driver, amplifier, and so on.

In one embodiment, demodulator 442 and modulator 446 may be combined ina single transceiver circuit. In another embodiment modulator 446 maymodulate a signal using backscatter. In another embodiment modulator 446may include an active transmitter. In yet other embodiments demodulator442 and modulator 446 may be part of processing block 444.

Circuit 424 additionally includes a memory 450 to store data 452. Atleast a portion of memory 450 is preferably implemented as a NonvolatileMemory (NVM), which means that data 452 is retained even when circuit424 does not have power, as is frequently the case for a passive RFIDtag.

In some embodiments, particularly in those with more than one antennaport, circuit 424 may contain multiple demodulators, rectifiers, PMUs,modulators, processing blocks, and/or memories.

In terms of processing a signal, circuit 424 operates differently duringa R→T session and a T→R session. The different operations are describedbelow, in this case with circuit 424 representing an IC of an RFID tag.

FIG. 5A shows version 524-A of components of circuit 424 of FIG. 4,further modified to emphasize a signal operation during a R→T sessionduring time interval 312 of FIG. 3. Demodulator 442 demodulates an RFsignal received from antenna contacts 432, 433. The demodulated signalis provided to processing block 444 as C_IN. In one embodiment, C_IN mayinclude a received stream of symbols.

Version 524-A shows as relatively obscured those components that do notplay a part in processing a signal during a R→T session. Rectifier andPMU 441 may be active, such as for converting RF power. Modulator 446generally does not transmit during a R→T session, and typically does notinteract with the received RF signal significantly, either becauseswitching action in section 435 of FIG. 4 decouples modulator 446 fromthe RF signal, or by designing modulator 446 to have a suitableimpedance, and so on.

Although modulator 446 is typically inactive during a R→T session, itneed not be so. For example, during a R→T session modulator 446 could beadjusting its own parameters for operation in a future session, and soon.

FIG. 5B shows version 524-B of components of circuit 424 of FIG. 4,further modified to emphasize a signal operation during a T-R sessionduring time interval 326 of FIG. 3. Processing block 444 outputs asignal C_OUT. In one embodiment, C_OUT may include a stream of symbolsfor transmission. Modulator 446 then modulates C_OUT and provides it toantenna segments such as segments 227 of RFID tag 220 via antennacontacts 432, 433.

Version 524-B shows as relatively obscured those components that do notplay a part in processing a signal during a T-R session. Rectifier andPMU 441 may be active, such as for converting RF power. Demodulator 442generally does not receive during a T→R session, and typically does notinteract with the transmitted RF signal significantly, either becauseswitching action in section 435 of FIG. 4 decouples demodulator 442 fromthe RF signal, or by designing demodulator 442 to have a suitableimpedance, and so on.

Although demodulator 442 is typically inactive during a T→R session, itneed not be so. For example, during a T→R session demodulator 442 couldbe adjusting its own parameters for operation in a future session, andso on.

In typical embodiments, demodulator 442 and modulator 446 are operableto demodulate and modulate signals according to a protocol, such as theGen2 Specification referenced above. In embodiments where circuit 424includes multiple demodulators and/or modulators, each may be configuredto support different protocols or different sets of protocols. Aprotocol specifies, in part, symbol encodings, and may include a set ofmodulations, rates, timings, or any other parameter associated with datacommunications.

FIG. 6 illustrates an identifier and a check code stored in an RFID tagIC according to embodiments.

Diagram 600 depicts memory 650, which may be included in tag IC 224. Insome embodiments memory 650 may be external to IC 224 (e.g., on anotherIC or on a different component on the tag) or integrated into acontroller or processing block (e.g., processing block 444). Memory 650may store a variety of data, such as an identifier 652 that providesinformation about IC 224, tag 220, and/or an item to which tag 220 isattached. For example, identifier 652 may identify the tag IC, tag, oritem, or may indicate some detail or attribute of the tag IC, tag, oritem. Identifier 652 may be but is not limited to a tag identifier(TID), a key identifier (KID), an item identifier such as an electronicproduct code (EPC), a universal product code (UPC), a stock-keeping unit(SKU) number, a unique item identifier (UII), a serialized global tradeidentification number (SGTIN), or any other suitable identifier.

Memory 650 may also store a check code 654, which is typically based onidentifier 652 and may be used to check the validity or correctness ofidentifier 652. Check code 654 may be a parity bit or bits, a checksum,a cyclic redundancy check, a hash function output, an error-correctingcode, or any other suitable code. As one of many possible examples,identifier 652 may be stored in one or more differential memory cellsand check code 654 may be stored in the complementary halves (i.e.complementary transistor or complementary bit) of the one or moredifferential memory cells. In some embodiments, check code 654 may beused to reconstruct the correct identifier if identifier 652 is found tobe incorrect or corrupt. In some embodiments, check code 654 may also(or instead) indicate if memory 650 (or a portion of memory 650) hasmalfunctioned or failed. For example, check code 654 may includeredundancy bit(s) that indicate whether one or more memory cells havefailed, or any other code that indicates whether physical memory isfunctioning properly.

Identifier 652 and check code 654 may be stored in memory 650 when IC224 is manufactured, when tag 220 is assembled, when tag 220 is printed,when tag 220 is attached to an item, or at any other suitable time.Check code 654 may be stored at the same time as identifier 652, at adifferent time from identifier 652, or computed by IC 224 itself. Forexample, an IC (or tag) manufacturer may generate and write identifier652 into memory 650. The manufacturer may then generate check code 654based on identifier 652 and write the generated check code 654 intomemory 650.

In some situations, identifier 652 and/or check code 654 may containerrors, latent errors, or be corrupted. For example, identifier 652and/or check code 654 may not be written strongly enough to memory(e.g., with insufficient voltage/current), and latent errors may occurwhen one or more bits of identifier 652 or check code 654 decay. Inanother example, manufacturing flaws may cause one or more bits ofmemory 650 to be defective or leaky, causing initially correct data toaccumulate errors over time. In another example, exposure to radiationmay cause written memory bits to flip or decay, introducing errors. Assuch, it may be desirable to have a tag IC perform a data integrityself-check procedure upon power-up. If the IC determines that its datais not corrupted, it may continue operation as normal. If the ICdetermines that its data is corrupted, it may indicate an error, performa self-correction procedure, and/or shut itself down, temporarily orpermanently.

FIG. 7A is a flowchart depicting a process 700 for identifier self-checkaccording to embodiments. In step 702, a tag IC (e.g., IC 224) receivessufficient power to operate. For example, the IC may extract operatingpower from an RF signal, such as may be transmitted by RFID readers. Insome embodiments, if the IC is coupled to a power source (e.g., as isthe case in a semi-passive or active tag), the IC may receive sufficientpower to operate independent of whether an RF signal is being received.Once the IC is powered, in step 704 it may retrieve an identifier (e.g.,identifier 652) and a check code (e.g., check code 654), both stored inmemory, and check to determine if the retrieved identifier correspondsto the retrieved check code. One of the many possible methods ofchecking involves the IC computing a new check code from the retrievedidentifier and comparing the new check code with the retrieved checkcode. If the new check code corresponds to the retrieved check code thenthe IC may determine that the identifier is correct, and continueoperation in step 706. On the other hand, if the new check code does notcorrespond to the retrieved check code then the IC may terminateoperation in step 708. The IC may terminate operation by powering down,killing itself (e.g., by asserting a “kill” flag associated with theIC), or not responding to external commands. For example, if the ICpowered up in response to receiving an RF signal transmitted by an RFIDreader, it may refrain from responding to a subsequent command from thereader.

FIG. 7B is a flowchart depicting another process 750 for identifierself-check according to embodiments. Steps 702, 704, and 706 in process750 are similar to the corresponding steps in process 700. However, inprocess 750, if the IC determines in step 704 that the retrievedidentifier does not correspond to the retrieved check code then the ICmay indicate an error in step 752. The IC may indicate an error by, forexample, backscattering an error or corruption code, writing the erroror corruption code to memory, rewriting a portion of its memory (e.g.,rewriting a memory portion such as a length field to subsequentlyexclude the corrupted portion of the identifier or the entire retrievedidentifier from a subsequent operation), asserting an error/corruptedidentifier flag, and/or adjusting an IC session flag. After indicatingan error in step 752 the IC may terminate operation (as in step 708 inprocess 700), or may continue operation (e.g., proceed to step 706).

As mentioned, in step 752 the IC may transmit or backscatter an error orcorruption code to indicate that the retrieved identifier does notcorrespond to the retrieved check code, such as in a reply to a readercommand. In some embodiments the IC may include an alternativeidentifier with the error/corruption code. In other embodiments the ICmay include the corrupted identifier with the error/corruption code. TheIC may include both the alternative and the corrupted identifier, orportions of one or both identifiers, or other information that may beuseful to the reader or to the reading system. For example, if the ICreceives a command from a reader requesting an item identifier that theIC has determined is corrupted then the IC may include anerror/corruption code, an alternative identifier such as a tag or ICidentifier, and/or the corrupted item identifier in the reply.

In some cases the error/corruption code may indicate the presence and/ornature of the included identifier(s). For example, the error code mayindicate that the reply includes identifier(s), and may also indicatewhether the included identifier(s) is an alternative identifier, thecorrupted identifier, or another code. In some embodiments, the errorcode may include protocol control information (e.g., protocol controlbits according to the Gen2 Specification) corresponding to identifierseither included in the reply or stored in memory. Protocol controlinformation associated with data may be used to indicate the length ofthe associated data. In some embodiments, an identifier that isdetermined to be corrupted may in effect be altered by adjusting itsassociated protocol control information. For example, a corruptedidentifier may be shortened or even set to zero length (in effect“erasing” it) by adjusting its associated protocol control information.The adjusted protocol control information may then be included in thereply to indicate that the requested identifier is corrupted. In someembodiments, the reply may also include an error-check code (e.g.,similar to check code 654) computed by the IC over the reply. Forexample, the IC may compute the error-check code based on one or morecomponents of the reply (e.g., the error/corruption code, thealternative identifier, the corrupted identifier, and/or any other codeincluded in the reply) and include the computed error-check code in thereply.

While the example above assumes that the corrupt code is the itemidentifier, the same procedure may be used if any other identifier orcode is corrupted. For example, if the reader requests a tag/ICidentifier that is determined to be corrupted then the IC may respondwith a different code (e.g., an item identifier or other suitable code).

FIG. 8 is a flowchart depicting a process 800 for identifier self-checkand correction according to embodiments. Process 800 is similar toprocesses 700 and 750 described above in FIGS. 7A and 78. However, inprocess 800, when the IC detects in step 704 that a retrieved identifierdoes not correspond to a retrieved check code then the IC may use theretrieved check code (e.g., check code 654) to reconstruct theidentifier in step 802. The IC may use the reconstructed identifier forthe purposes of replying to a reader command, for overwriting orcorrecting the stored identifier in memory, for notifying a reader aboutthe nature of the error, or for any other purpose. The IC may thenproceed to step 706 where it continues operation.

In some embodiments, upon determining that a retrieved identifier doesnot correspond to a retrieved check code, the IC may first attempt tore-retrieve the identifier and the check code from the memory todetermine if the mismatch is due to an error during the retrievalprocess. If the re-retrieved identifier corresponds to the re-retrievedcheck code, then the IC may continue operation (e.g., step 706) by, forexample, replying to a received reader command. If the re-retrievedidentifier still does not correspond to the re-retrieved check code thenthe IC may proceed to terminate operation (e.g., step 708), indicate anerror (e.g., step 752), or attempt to reconstruct the identifier (e.g.,step 802). In some embodiments, the IC may also (or instead) attempt topower-cycle the memory or the IC itself by interrupting and thenrestoring power to the memory or IC.

The steps described in processes 700, 750, and 800 are for illustrationpurposes only. An RFID IC identifier self-check may be performedemploying additional or fewer steps and in different orders using theprinciples described herein. Of course the order of the steps may bemodified, some steps eliminated, or other steps added according to otherembodiments. For example, an IC that has determined that a storedidentifier does not correspond to a stored check code may indicate anerror (as in step 752), reconstruct the identifier (as in step 802),continue operation (as in step 706), and/or terminate operation (as instep 708), in any order.

In some embodiments, pan of the RFID IC identifier self-check processmay be performed by an RFID reader. For example, a reader may determinethat an IC identifier and a check code stored on the IC do notcorrespond (e.g., by reading the identifier and check code from the ICand/or receiving an error indication from the IC). In response, thereader may log the incorrect identifier and/or check code (e.g., bystoring them locally and/or uploading them to a network), instruct theIC to terminate operation (e.g., as in step 708), reconstruct theidentifier (e.g., as in step 802), and/or kill the tag. In someembodiments the reader may write a reconstructed identifier to the IC.The identifier may be reconstructed by the reader (e.g., based on thecheck code), may have been previously stored on the reader, or receivedfrom a remote location (e.g., a networked server).

The foregoing detailed description has set forth various embodiments ofthe devices and/or processes via the use of block diagrams and/orexamples. Insofar as such block diagrams and/or examples contain one ormore functions and/or aspects, it will be understood by those within theart that each function and/or aspect within such block diagrams orexamples may be implemented, according to embodiments formed,individually and/or collectively, by a wide range of hardware, software,firmware, or virtually any combination thereof.

The present disclosure is not to be limited in terms of the particularembodiments described in this application, which are intended asillustrations of various aspects. Many modifications and variations canbe made without departing from its spirit and scope, as will be apparentto those skilled in the art. Functionally equivalent methods andapparatuses within the scope of the disclosure, in addition to thoseenumerated herein, will be apparent to those skilled in the art from theforegoing descriptions. Such modifications and variations are intendedto fall within the scope of the appended claims. The present disclosureis to be limited only by the terms of the appended claims, along withthe full scope of equivalents to which such claims are entitled. It isto be understood that this disclosure is not limited to particularmethods, configurations, antennas, transmission lines, and the like,which can, of course, vary. It is also to be understood that theterminology used herein is for the purpose of describing particularembodiments only, and is not intended to be limiting.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood that if a specific number of anintroduced claim recitation is intended, such an intent will beexplicitly recited in the claim, and in the absence of such recitationno such intent is present. For example, as an aid to understanding, thefollowing appended claims may contain usage of the introductory phrases“at least one” and “one or more” to introduce claim recitations.However, the use of such phrases should not be construed to imply thatthe introduction of a claim recitation by the indefinite articles “a” or“an” limits any particular claim containing such introduced claimrecitation to embodiments containing only one such recitation, even whenthe same claim includes the introductory phrases “one or more” or “atleast one” and indefinite articles such as “a” or “an” (e.g., “a” and/or“an” should be interpreted to mean “at least one” or “one or more”); thesame holds true for the use of definite articles used to introduce claimrecitations. In addition, even if a specific number of an introducedclaim recitation is explicitly recited, those skilled in the art willrecognize that such recitation should be interpreted to mean at leastthe recited number (e.g., the bare recitation of“two recitations,”without other modifiers, means at least two recitations, or two or morerecitations).

Furthermore, in those instances where a convention analogous to “atleast one of A, B, and C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention (e.g., “a system having at least one of A, B, and C”would include but not be limited to systems that have A alone, B alone,C alone, A and B together, A and C together, B and C together, and/or A,B, and C together, etc.). It will be further understood that virtuallyany disjunctive word and/or phrase presenting two or more alternativeterms, whether in the description, claims, or drawings, should beunderstood to contemplate the possibilities of including one of theterms, either of the terms, or both terms. For example, the phrase “A orB” will be understood to include the possibilities of “A” or “B” or “Aand B.”

As will be understood by one skilled in the art, for any and allpurposes, such as in terms of providing a written description, allranges disclosed herein also encompass any and all possible subrangesand combinations of subranges thereof. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed herein canbe readily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art all languagesuch as “up to,” “at least,” “greater than,” “less than,” and the likeinclude the number recited and refer to ranges which can be subsequentlybroken down into subranges as discussed above. Finally, as will beunderstood by one skilled in the art, a range includes each individualmember.

I claim:
 1. A method for a Radio Frequency Identification (RFID)integrated circuit (IC) to indicate a corrupted identifier, the methodcomprising: upon extracting an operating power from a received RFsignal, retrieving a first identifier and a check code from an ICnonvolatile memory, the check code based on and used to check acorrectness of the first identifier; determining that the check codedoes not correspond to the first identifier and that the firstidentifier is therefore corrupted; adjusting protocol controlinformation associated with the first identifier, wherein the unadjustedprotocol control information indicates that the first identifier has anonzero length and the adjusted protocol control information indicatethat the first identifier has a zero length; and upon subsequentlyreceiving a command requesting the first identifier, transmitting areply to the command including at least the adjusted protocol controlinformation.
 2. The method of claim 1, in which the first identifierincludes a code indicating at least one of an attribute of the IC and anattribute of an item associated with the IC.
 3. The method of claim 1,in which at least one bit of the check code is stored in a complementaryhalf of a differential memory cell.
 4. The method of claim 1, furthercomprising power-cycling one of the IC and the memory upon determiningthat the first identifier is corrupted.
 5. The method of claim 1, inwhich the check code includes at least one of: at least onememory-redundancy bit; at least one parity bit; a checksum; a cyclicredundancy check; a hash function output; and an error-correcting code.6. The method of claim 1, further comprising: computing a cyclicredundancy check based on the reply; and including the cyclic redundancycheck in the reply.
 7. The method of claim 1, further comprising, upondetermining that the first identifier is corrupted, at least one of:asserting a kill flag of the IC, writing an error code to the memory,asserting an error flag in the memory, adjusting a session flag of theIC, and rewriting at least a portion of the memory.
 8. The method ofclaim 1, further comprising including the first identifier in the reply.9. A method for a Radio Frequency Identification (RFID) integratedcircuit (IC) to avoid sending a corrupted identifier, the methodcomprising: upon extracting an operating power from a received RFsignal, retrieving a first identifier and a check code from an ICnonvolatile memory, the check code based on and used to check acorrectness of the first identifier; determining that the check codedoes not correspond to the first identifier and that the firstidentifier is therefore corrupted; reconstructing a correct identifierfrom at least the first identifier and the check code; and uponsubsequently receiving a command requesting the first identifier,transmitting a reply to the command including the correct identifier.10. The method of claim 9, in which the first identifier includes a codeindicating at least one of an attribute of the IC and an attribute of anitem associated with the IC.
 11. The method of claim 9, in which atleast one bit of the check code is stored in a complementary half of adifferential memory cell.
 12. The method of claim 9, further comprisingpower-cycling one of the IC and the memory upon determining that thefirst identifier is corrupted.
 13. The method of claim 9, in which thecheck code includes at least one of: at least one memory-redundancy bit;at least one parity bit; a checksum; a cyclic redundancy check; a hashfunction output; and an error-correcting code.
 14. The method of claim9, further comprising: computing a cyclic redundancy check based on thereply; and including the cyclic redundancy check in the reply.
 15. Themethod of claim 9, further comprising, upon determining that the firstidentifier is corrupted, at least one of: asserting a kill flag of theIC, writing an error code to the memory, asserting an error flag in thememory, adjusting a session flag of the IC, and overwriting the firstidentifier with the correct identifier.